Methods of extracting volatiles from ceramic green bodies

ABSTRACT

Methods of producing a ceramic article include heating the ceramic green body containing a quantity of one or more organic materials to extract only a fraction of the organic materials from the ceramic green body by exposing the ceramic green body to a process atmosphere which is heated to a hold temperature of from 225° C. to about 400° C. and has from 2% to 7% O2 by volume of the process atmosphere. The method further includes cooling the ceramic green body to a temperature of below 200° C., exposing the ceramic green body to a higher concentration of O2 than in the process atmosphere of the heating step, and firing the ceramic green body to form the ceramic article. Volatile extraction units for implementing the methods are also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application under 35 U.S.C. § 371of International Application No. PCT/US2018/042819 filed on Jul. 19,2018 which claims the benefit of priority under 35 U.S.C. § 119 of U.S.Provisional Application Ser. No. 62/535,549, filed on Jul. 21, 2017, thecontents of which are relied upon and incorporated herein by referencein their entireties.

BACKGROUND Field

The present specification generally relates to the manufacture ofceramic articles and, more particularly, to methods for extractingvolatiles from ceramic green bodies prior to firing.

Technical Background

Ceramic articles composed of refractory ceramic materials such ascordierite, silicon carbide, aluminum titanate and the like are widelyused for the manufacture of catalytic substrates and particulatefilters. Such substrates and filters are employed for the removal ofpollutants such as carbon monoxide, nitrogen and sulfur oxides, unburnedhydrocarbons and particulates such as soot from combustion engineexhaust gases or stack gases from industrial combustion processes.

SUMMARY

According to one aspect, a method of producing a ceramic articlecomprises heating a ceramic green body containing a quantity of one ormore organic materials to extract only a fraction of the organicmaterials from the ceramic green body by heating the green body byexposing the ceramic green body to a process atmosphere which is heatedto a hold temperature of from 225° C. to 400° C. and has from 2% to 7%O₂ by volume of the process atmosphere. The method further comprisescooling the ceramic green body to a temperature of below 200° C.,exposing the ceramic green body to a higher concentration of O₂ than inthe process atmosphere of the heating step, and firing the ceramic greenbody to form the ceramic article.

According to another aspect, a method of producing a ceramic articlecomprises placing a ceramic green body comprising organic materials in avolatile extraction unit, heating the ceramic green body by exposing theceramic green body to a process atmosphere within the volatileextraction unit heated to a first temperature and having a concentrationof O₂ of from 2% to 7% O₂ by volume of the process atmosphere to removeat least some of the organic materials from the ceramic green body, andheating the process atmosphere to a second temperature to remove atleast an additional amount of the organic materials from the ceramicgreen body. The first temperature is from 140° C. to 180° C. and thesecond temperature is from 225° C. to 400° C. The method furthercomprises cooling the ceramic green body to a temperature of below 200°C., increasing an amount of O₂ in the process atmosphere, and firing theceramic green body to form the ceramic article.

According to yet another aspect, a method of forming a ceramic articlecomprises providing a ceramic green body comprising organic materials,and heating the ceramic green body to extract at least a portion of theorganic materials. The ceramic green body is heated by exposing theceramic green body to a process atmosphere heated at a rate of from 50°C./h to 130° C./h to a temperature of from 225° C. to 400° C. and havingfrom 2% to 7% O₂ by volume of the process atmosphere. The method furthercomprises cooling the ceramic green body to a temperature below 200° C.,increasing an amount of O₂ in the process atmosphere, and firing theceramic green body to form the ceramic article.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from that description or recognized by practicing theembodiments described herein, including the detailed description whichfollows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description describe various embodiments ofmethods and apparatuses for forming ceramic articles and are intended toprovide an overview or framework for understanding the nature andcharacter of the claimed subject matter. The accompanying drawings areincluded to provide a further understanding of the various embodiments,and are incorporated into and constitute a part of this specification.The drawings illustrate the various embodiments described herein, andtogether with the description serve to explain the principles andoperations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram of an example ceramic article production linefor forming a ceramic article in accordance with one or more embodimentsdescribed herein;

FIG. 2 schematically depicts an example volatile extraction unit forextracting organic materials from a ceramic green body in accordancewith one or more embodiments described herein;

FIG. 3 graphically depicts temperature (left-hand vertical axis), lowerflammability limit levels (left-hand vertical axis), modeled weight lossfor a ceramic green body, measured weight loss for a ceramic green body,and weight loss rate (right-hand vertical axis) as a function of time(horizontal axis) in accordance with one or more embodiments describedherein;

FIG. 4 graphically depicts temperature (in ° C.; left-hand verticalaxis), LFL level (in %; right-hand vertical axis), and oxygenconcentration (in %; right hand vertical axis) are shown as a functionof time (in hours; horizontal axis) for an example volatile extractioncycle in accordance with one or more embodiments described herein; and

FIG. 5 graphically depicts LFL levels (in %; right-hand vertical axis)and average temperature (in ° C.; left-hand vertical axis) of a firingcycle for ceramic green bodies subjected to a volatile extraction cycleas a function of time (in hours; horizontal axis) in accordance with oneor more embodiments described herein and for ceramic green bodies notsubjected to a volatile extraction cycle in accordance with one or moreembodiments described herein.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of methodsfor producing ceramic articles comprising extracting at least someorganic materials prior to firing, examples of which are illustrated inthe accompanying drawings. Whenever possible, the same referencenumerals will be used throughout the drawings to refer to the same orlike parts.

One embodiment of a ceramic article production line is schematicallydepicted in FIG. 1 , and is designated generally throughout by thereference numeral 100. The ceramic article production line 100 maygenerally comprise an extruder 102 for forming a ceramic green body fromceramic batch materials, a volatile extraction unit 104 for extractingat least some organic material, or volatiles, from the ceramic greenbody, and a kiln 106 for firing the ceramic green body to form a ceramicarticle. The volatile extraction unit 104 may comprise a processatmosphere having a low oxygen concentration and, by heating the ceramicgreen body, extracts at least some of the organic materials from theceramic green body. Accordingly, because high volatile concentrations,or portions of the organic materials, have already been released in thevolatile extraction unit 104, the ceramic green body may be fired in thekiln 106 for a shorter period of time and without atmospheric controls,thermal oxidizers, and/or lower flammability limit (LFL) and limitedoxygen concentration (LOC) controls.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order, nor that with any apparatus specificorientations be required. Accordingly, where a method claim does notactually recite an order to be followed by its steps, or that anyapparatus claim does not actually recite an order or orientation toindividual components, or it is not otherwise specifically stated in theclaims or description that the steps are to be limited to a specificorder, or that a specific order or orientation to components of anapparatus is not recited, it is in no way intended that an order ororientation be inferred, in any respect.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to “a” component includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

As used herein, the terms “unfired extruded body,” “green body,” “greenceramic body,” or “ceramic green body” refer to an unsintered body,part, or ware before firing, unless otherwise specified. The terms“batch mixture,” “ceramic precursor batch,” “green composition,” and“green batch material” refer to the mixture of materials that are usedto form the green body by extrusion, unless otherwise specified. Theunfired extruded body and batch mixture contain a vehicle, such aswater, and typically comprise inorganic components, and can compriseother materials such as binders, pore formers, stabilizers,plasticizers, and the like.

As used herein, “firing” refers to thermal processing of the green bodyat an elevated temperature to form a ceramic material or a ceramic body.

As used herein, a “wt %,” “weight percent,” or “percent by weight” of aninorganic or organic component, unless specifically stated to thecontrary, is based on the total weight of the inorganics in which thecomponent is included. Organic components are specified herein as superadditions based upon 100% of the inorganic components used.

Specific and preferred values disclosed for components, ingredients,additives, reactants, constants, scaling factors, and like aspects, andranges thereof, are for illustration only. They do not exclude otherdefined values or other values within defined ranges. The compositions,apparatus, and methods of the disclosure include those having any valueor combination of the values, specific values, or ranges thereofdescribed herein. Any ranges of values set forth in this specificationcontemplate all values within the range and are to be construed assupport for claims reciting any sub-ranges having endpoints which arereal number values within the specified range in question. By way of ahypothetical illustrative example, a recitation in this disclosure of arange of from about 1 to about 5 shall be considered to support claimsto any of the following ranges: 1-5; 1-4; 1-3; 1-2; 2-5; 2-4; 2-3; 3-5;3-4; and 4-5.

During firing of ceramic bodies, organic materials (such as organiccomponents or additives) vaporize into the kiln atmosphere. These vaporscan be volatile and can comprise hydrogen and carbon monoxide, which arecombustible and can become flammable leading to dangerous conditionsduring processing. The National Fire Protection Agency (NFPA) requiresmanufacturers of ceramic products with organic additive systems tomaintain kiln atmospheres at specific levels of volatile organiccompounds to prevent uncontrolled combustion, deflagration ordetonation. Although atmospheric controls can be incorporated intofiring kilns to meet NFPA requirements, firing cycles that last severalhours or longer can result in large capital expenses on a per cyclebasis. The methods disclosed herein may reduce the length of firingcycles as well as reduce or eliminate the need for atmospheric controlsin firing cycles by extracting at least some organic materials fromceramic green bodies prior to firing.

Referring to FIG. 1 , one embodiment of a ceramic article productionline 100 for forming a ceramic article 107 is schematically depicted.The ceramic article production line 100 generally comprises an extruder102 for forming a ceramic green body from a ceramic batch mixture 101, avolatile extraction unit 104 located downstream of the extruder 102 forextracting at least some organic material from the ceramic green body,and a kiln 106 for firing the ceramic green body after at least someorganic material has been extracted in the volatile extraction unit 104to form the ceramic article 107. Although various embodiments hereindescribe forming a ceramic green body using an extruder, it iscontemplated that the ceramic green body may be formed by any suitabletechnique, including, by way of example and not limitation, molding,pressing, or casting.

The ceramic batch mixture 101 from which the ceramic green body isformed comprises ceramic-forming raw materials. The ceramic-forming rawmaterials are typically inorganic materials. As an example, theceramic-forming raw materials may be cordierite-forming raw materials,aluminum titanate-forming raw materials, silicon carbide-forming rawmaterials, alumina-forming raw materials, alumina, silica, magnesia,titania, aluminum-containing ingredients, silicon-containingingredients, titanium-containing ingredients, and the like.

Cordierite-forming raw materials may comprise, for example, at least onemagnesium source, at least one alumina source, and at least one silicasource. The cordierite-forming raw materials may further comprise one ormore of clay and titania, as well as alkaline earth metals and oxides.

In the embodiments described herein, sources of magnesium comprise, butare not limited to, magnesium oxide or other materials having low watersolubility that, when fired, convert to MgO, such as Mg(OH)₂, MgCO₃, andcombinations thereof. For example, the source of magnesium may be talc(Mg₃Si₄O₁₀(OH)₂), comprising calcined and/or uncalcined talc, and coarseand/or fine talc.

Sources of alumina comprise, but are not limited to, powders that, whenheated to a sufficiently high temperature in the absence of other rawmaterials, will yield substantially pure aluminum oxide. Examples ofsuitable alumina sources may comprise alpha-alumina, a transitionalumina such as gamma-alumina or rho-alumina, hydrated alumina oraluminum trihydrate, gibbsite, corundum (Al₂O₃), boehmite (AlO(OH)),pseudoboehmite, aluminum hydroxide (Al(OH)₃), aluminum oxyhydroxide, andmixtures thereof.

Silica may be present in its pure chemical state, such as α-quartz orfused silica. Sources of silica may comprise, but are not limited to,non-crystalline silica, such as fused silica or sol-gel silica, siliconeresin, low-alumina substantially alkali-free zeolite, diatomaceoussilica, kaolin, and crystalline silica, such as quartz or cristobalite.Additionally, the sources of silica may further comprise, but are notlimited to, silica-forming sources that comprise a compound that formsfree silica when heated. For example, silicic acid or a siliconorganometallic compound may form free silica when heated.

Hydrated clays used in cordierite-forming raw materials can comprise, byway of example and not limitation, kaolinite (Al₂(Si₂O₅)(OH)₄),halloysite (Al₂(Si₂O₅)(OH)₄.H₂O), pyrophylilite (Al₂(Si₂O₅)(OH)₂),combinations or mixtures thereof, and the like.

Aluminum titanate-forming raw materials may comprise, for example, analumina source, a silica source, and a titania source. The titaniasource can in one aspect be a titanium dioxide composition, such asrutile titania, anatase titania, or a combination thereof. The aluminasource and silica source may be selected from the sources of alumina andsilica described hereinabove. Exemplary non-limiting inorganic batchcomponent mixtures suitable for forming aluminum titanate include thosedisclosed in U.S. Pat. Nos. 4,483,944; 4,855,265; 5,290,739; 6,620,751;6,942,713; 6,849,181; 7,001,861; and 7,294,164, each of which is herebyincorporated by reference.

Silicon carbide-forming raw materials may comprise, for example, finelypowdered silicon metal, a carbon precursor, and powderedsilicon-containing fillers. The carbon precursor may be, for example, awater soluble crosslinking thermoset resin having a viscosity of lessthan about 1000 centipoise (cp). The thermoset resin utilized may be ahigh carbon yield resin in an amount such that the resultant carbon tosilicon ratio in the batch mixture is about 12:28 by weight, thestoichiometric ratio of Si—C needed for formation of silicon carbide.Suitable silicon-containing fillers comprise silicon carbide, siliconnitride, mullite or other refractory materials. Exemplary non-limitinginorganic batch component mixtures suitable for forming silicon carbideinclude those disclosed in U.S. Pat. Nos. 6,555,031 and 6,699,429, eachof which is hereby incorporated by reference.

Aluminum oxide-forming raw materials may comprise Al₂O₃ and/or aluminumoxide-forming ingredients.

In addition to the ceramic-forming raw materials, the ceramic batchmixture 101 comprises organic materials that may comprise lubricants,surfactants, binders, and/or one or more pore-forming materials. Theterm “organic materials,” as used herein, excludes the amount ofsolvents, such as water, included in various batch compositions. Theorganic materials are used to form a flowable dispersion that has arelatively high loading of the ceramic material. The lubricants andsurfactants are chemically compatible with the inorganic components, andprovide sufficient strength and stiffness to allow handling of theceramic green body. In embodiments, the ceramic batch mixture 101 mayhave organic materials in percent by weight of the inorganic components,by super addition, from about 1% to about 25% or even from about 2% toabout 20%. In some embodiments, the ceramic batch mixture 101 may haveorganic materials in percent by weight of the inorganic components, bysuper addition, from about 5% to about 15%, from about 7% to about 12%,or even from about 9% to about 10%. In some embodiments, the ceramicbatch mixture 101 may have organic materials in percent by weight of theinorganic components, by super addition, from about 5% to about 11%, orabout 7%.

The organic materials, in some embodiments, may comprise a binder and atleast one pore-forming material. In embodiments, the organic binder ispresent in the composition as a super addition in an amount in the rangeof from 0.1% to about 10.0% by weight of the inorganic ceramic batchmixture. Binders may comprise, but are not limited to,cellulose-containing components such as methylcellulose, ethylhydroxyethylcellulose, hydroxybutyl methylcellulose, hydroxymethylceIlulose,hydroxypropyl methylcellulose, hydroxyethyl methylcellulose,hydroxybutylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,sodium carboxy methylcellulose, and mixtures thereof. Methylcelluloseand/or methylcellulose derivatives, such as hydroxypropylmethylcellulose, are especially suited as organic binders.

Pore formers are fugitive particulate material which is vaporized bycombustion during drying and heating of the ceramic green body leavingbehind a larger porosity than would otherwise be obtained. Pore-formingmaterials can comprise, for example, carbon (e.g., graphite, activatedcarbon, petroleum coke, and carbon black), starch (e.g., corn, barley,bean, potato, rice, tapioca, pea, sago palm, wheat, canna, and walnutshell flour), polymers (e.g., polybutylene, polymethylpentene,polyethylene, polypropylene, polystyrene, polyamides (nylons), epoxies,acrylonitrile butadiene styrene (ABS), acrylics, and polyesters (PET)),hydrogen peroxides, and/or resins, such as phenol resin. In embodimentscomprising pore formers, one or more pore-forming materials may beemployed. For example, in embodiments, a combination of a polymer and astarch may be used as the pore former. In the embodiments describedherein, the ceramic batch mixture may comprise from about 10% to about35% by weight of an organic pore former. In the embodiments describedherein the organic pore formers generally have a median particle sized₅₀ less than or equal to 20 microns. In some embodiments, the organicpore formers have a median particle size also less than or equal to 15microns or even a median particle size d₅₀ less than or equal to 10microns. It should be understood that the particular size and amount ofpore former may be selected based on a desired porosity and pore sizeddistribution in the finished ceramic article.

The lubricant provides fluidity to the ceramic precursor batch and aidsin shaping the ceramic precursor batch while also allowing the batch toremain sufficiently stiff during the forming (i.e., the extruding)process. The lubricant can comprise, for example, mineral oils distilledfrom petroleum, synthetic and semi-synthetic base oils, including GroupII and Group III paraffinic base oils, polyalphaolefins, alphaolefins,and the like. In various embodiments, the lubricant is apolyalphaolefin. Exemplary polyalphaolefins suitable for use includethose sold under the trade name DURASYN®, including but not limited toDURASYN® 162 and DURASYN® 164, and SILKFLO®, including but not limitedto SILKFLO® 362, available from INEOS Group AG (Switzerland). Otherexemplary lubricants suitable for use include those sold under the tradenames NEXBASE®, including but not limited to NEXBASE® 3020 (Neste Oil,Finland), and PARAFLEX™, including but not limited to PARAFLEX™ HT5(Petro-Canada, Canada). In various embodiments, the lubricant is presentin an amount of at least 3 wt % of the inorganic components, by superaddition.

Organic surfactants may adsorb to the inorganic particles, keep theinorganic particles in suspension, and prevent clumping of the inorganicparticles. The organic surfactant can comprise, for example, C₈-C₂₂fatty acids and/or their ester or alcohol derivatives, such as stearic,lauric, linoleic, oleic, myristic, palmitic, and palmitoleic acids, soylecithin, and mixtures thereof. In various embodiments, the organicsurfactant is present in an amount of at least 0.3 wt % of the inorganiccomponents, by super addition.

In various embodiments, solvents may be added to the batch mixture tocreate a ceramic paste (precursor or otherwise) from which the ceramicgreen body is formed. In embodiments, the solvents may compriseaqueous-based solvents, such as water or water-miscible solvents. Insome embodiments, the solvent is water. The amount of aqueous solventpresent in the ceramic precursor batch may range from about 20 wt % toabout 50 wt % of the total weight of the batch mixture.

According to various embodiments, the organic materials are added to atleast one inorganic component and mixed to form the ceramic batchmixture 101. The ceramic batch mixture 101 may be made by conventionaltechniques. By way of example, the inorganic components may be combinedas powdered materials and intimately mixed to form a substantiallyhomogeneous batch. The organic materials and/or solvent may be mixedwith inorganic components individually, in any order, or together toform a substantially homogeneous batch. Of course, other suitable stepsand conditions for combining and/or mixing inorganic components andorganic materials together to produce a substantially homogeneous batchmay be used. For example, the inorganic components and organic materialsmay be mixed by a kneading process to form a substantially homogeneousbatch mixture.

In various embodiments, the ceramic batch mixture 101 is shaped orformed into a structure using conventional forming means, such asmolding, pressing, casting, extrusion, and the like. According to theembodiment depicted in FIG. 1 , the ceramic batch mixture 101 isextruded using the extruder 102 to form a ceramic green body. Theextruder 102 may be a hydraulic ram extrusion press, a two stagede-airing single auger extruder, or a twin screw mixer with a dieassembly attached to the discharge end of the extruder 102, depending onthe particular embodiment. The ceramic batch mixture 101 may be extrudedat a predetermined temperature and velocity.

In various embodiments, the ceramic batch mixture 101 is formed into ahoneycomb structure. The honeycomb structure may comprise a webstructure having a plurality of cells separated by cell walls. However,it is contemplated that the ceramic green body may be in a form otherthan a honeycomb structure.

In various embodiments, after the ceramic green body is formed, at leastsome of the organic materials or volatiles are extracted in the volatileextraction unit 104. As will be described in greater detail, thevolatile extraction unit 104 may be a kiln that comprises at least atemperature sensor for sensing a temperature within the volatileextraction unit 104, a temperature control unit communicatively coupledto the temperature sensor and configured to adjust the temperaturewithin the volatile extraction unit 104, a gas injection port forinjecting a low oxygen content gas into the volatile extraction unit104, and an exhaust system for releasing the volatiles from the volatileextraction unit 104. In various embodiments, the volatile extractionunit 104 may further comprise thermal oxidizers, lower flammabilitylimit (LFL) controls, and/or limited oxygen concentration (LOC)controls. In practice, the formed ceramic green body is transferred intothe volatile extraction unit 104, where it is heated to a temperaturesufficient to volatilize at least some of the organic materials in theceramic green body in a low oxygen process atmosphere.

In embodiments, at least 50% of the volatiles are extracted from theceramic green body during processing in the volatile extraction unit104. In some embodiments, at least 75% of the volatiles are extractedfrom the ceramic green body. In other words, in various embodiments, theceramic green body is heated in the volatile extraction unit 104 for atime sufficient to volatilize at least 75% of volatiles in the organicmaterials.

After at least some of the organic materials are volatilized and removedfrom the ceramic green body, the ceramic green body is transferred tothe kiln 106, where it is fired at a selected temperature under suitableatmosphere and for a time dependent upon the composition, size, andgeometry of the ceramic green body to result in a fired, porous ceramicarticle 107. The kiln may be, by way of example and not limitation, atunnel kiln, a fuel or direct fired kiln, an electric kiln, or amicrowave-assisted kiln.

As shown in FIG. 1 , in various embodiments, the kiln 106 is a differentkiln from the volatile extraction unit 104 and the ceramic green bodiesare preferably transferred from volatile extraction unit 104 to kiln 106after the ceramic green bodies are processed in the volatile extractionunit. In other embodiments, kiln 106 and volatile extraction unit 104are the same kiln, which both extracts volatiles from the ceramic greenbodies and then fires the ceramic green bodies.

Firing times and temperatures depend on factors such as the compositionand amount of material in the ceramic green body and the type ofequipment used to fire the ceramic green body. For example and withoutlimitation, firing temperatures for forming cordierite may range fromabout 1300° C. up to about 1450° C., with holding times at the peaktemperatures ranging from about 1 hour to about 8 hours and total firingtimes that may range from about 20 hours up to about 85 hours. Duringfiring, temperatures in the firing process atmosphere may be increasedat a rate greater than 50° C./hr. Suitable firing processes may includethose described in U.S. Pat. Nos. 6,287,509, 6,099,793, or 6,537,481,each of which is incorporated by reference in its entirety. Duringfiring, remaining organic materials (preferably all remaining organicmaterials) in the ceramic green body may be removed from the ceramicgreen body. When fired to form a ceramic article, the honeycombstructures can be used as flow-through substrates such as for catalyticconverters or particulate filters for internal combustion systems, suchas wall flow filters (that may be comprised of plugged honeycomb bodies)for example.

In various embodiments, because at least some of the organic materialshave been removed from the ceramic green body prior to firing, the kiln106 may be a kiln that is devoid of atmospheric controls (including, butnot limited to, active oxygen controls, particulate organic carbon (POC)or process N₂), thermal oxidizers, lower flammability limit (LFL)controls, and/or limited oxygen concentration (LOC) controls. Moreover,in various embodiments, the kiln 106 may employ lower levels of volumeexchanges of gases within the kiln as compared to kilns employed inconventional firing processes. In some embodiments, because it lacksatmospheric controls, the kiln 106 has a process atmosphere that ispermitted to freely fluctuate.

FIG. 2 schematically depicts a volatile extraction unit 104 for use withthe methods described herein in greater detail. As shown in FIG. 2 , thevolatile extraction unit 104 comprises a gas injection port 202 forinjecting a low oxygen content gas into the volatile extraction unit 104and an exhaust port 204 through which volatiles may be exhausted fromthe volatile extraction unit 104. The volatile extraction unit 104further comprises a lower flammability limit (LFL) detector 206, such asModel 670 Series LFL Detector available from Control InstrumentsCorporation (Fairfield, N.J.), for continuously measuring and monitoringthe LFL level in the volatile extraction unit 104. As used herein, the“lower flammability limit,” or LFL, refers to the minimum concentrationof volatile combustibles in which a flame can be propagated. LFL isexpressed as a percentage. In particular, a LFL level of about 70% meansthat the atmosphere contains a combustible volatile compound or mixtureof combustible volatile compounds in a concentration equal to 70% of theLFL of the mixture. At 100% LFL, the atmosphere can sustain andpropagate a flame. Although the volatile extraction unit 104 in FIG. 2comprises a LFL detector 206, in other embodiments, a flame ionizationdetector, mass spectrometer, or other measurement device configured tomeasure the volatiles in the process atmosphere may be employed.

As will be described in greater detail, the LFL detector 206 may provideinformation regarding the LFL level for use in determining a period oftime at which the ceramic green body will be held at a hold temperatureto volatilize at least some of the organic material. However, in someembodiments, the hold time may be determined according to a rate ofweight loss. In such embodiments, the volatile extraction unit 104 maycomprise a scale or other sensor configured to measure the weight of theceramic green body during the volatile extraction cycle in addition toor as an alternative to the LFL detector 206. As will be describedbelow, the scale may be used to measure a weight of the ceramic greenbody during the volatile extraction cycle, which may be used todetermine a weight loss or rate of weight loss during the volatileextraction cycle. In embodiments including a scale, the weight loss orrate of weight loss may be utilized to determine an amount of organicmaterial extracted from the ceramic green body.

In various embodiments, in addition to the LFL detector 206, thevolatile extraction unit 104 may further comprise thermal oxidizersand/or LFL or limiting (minimum) oxygen concentration (LOC) controls(not shown). As used herein, the “limiting oxygen concentration,” orLOC, is the minimum O₂ concentration in a mixture, such as anatmosphere, that will propagate flame.

For example, in some embodiments, a thermal oxidizer, including, but notlimited to, a recuperative thermal oxidizer, a regenerative thermaloxidizer, a regenerative catalytic thermal oxidizer, or a catalyticthermal oxidizer, may be coupled with the exhaust port 204 to reduce thevolatile levels or even destroy volatiles in an air stream passingthrough the exhaust port 204. The thermal oxidizer may comprise one ormore external heating sources, such as a burner, to raise thetemperature of the air stream entering the thermal oxidizer. In otherembodiments, the thermal oxidizer may utilize waste heat generated bythe ceramic article production line 100 to elevate the temperature ofthe air stream passing through the exhaust port 204. For example, heatgenerated by the kiln 106 may be utilized by the thermal oxidizer insome embodiments. In embodiments in which a thermal oxidizer isemployed, the treated air stream exiting the thermal oxidizer hasreduced volatile levels as it exits to the atmosphere as compared to theair stream entering the thermal oxidizer.

In FIG. 2 , the LFL detector 206 is coupled to a controller 208. Thecontroller 208 is communicatively coupled to a heat source 210 and a gassource 212. In one embodiment, the controller 208 may be a programmablelogic controller (PLC), although the controller 208 may be any suitablecomputing device. Moreover, although FIG. 2 depicts a single controller208 that is coupled to the LFL detector 206, the heat source 210, andthe gas source 212, it is contemplated that other embodiments may employmore than one controller, each configured to perform a portion of thefunctions of the controller 208. For example, in some embodiments, atemperature control unit may be communicatively coupled to the heatsource 210 to adjust the temperature within the volatile extraction unit104, while a separate process atmosphere control unit may becommunicatively coupled to the gas source 212 to adjust theconcentration of various components within the process atmosphere.

The controller 208 may comprise one or more processors capable ofexecuting machine readable instructions stored in a memory component,such as an integrated circuit, a microchip, a computer, or any othercomputing device. The memory component may be configured as a volatileand/or nonvolatile non-transitory computer readable medium and, as such,may comprise random access memory (including SRAM, DRAM, and/or othertypes of random access memory), flash memory, registers, compact discs(CD), digital versatile discs (DVD), magnetic disks, and/or other typesof storage components. Additionally, the memory component may beconfigured to store, among other things, operation logic. The memorycomponent may also store data, such as data captured by the LFL detector206 or externally acquired data, for determining whether a suitableamount of organic material has been volatilized and extracted from theceramic green body or for adjusting the O₂ concentration or thetemperature within the volatile extraction unit 104.

In embodiments, the controller 208 further preferably comprises acommunication pathway that may provide signal interconnectivity betweenvarious components coupled to the controller 208, including but notlimited to, the LFL detector 206, the heat source 210, and the gassource 212. The communication pathway may be formed from any medium thatis capable of transmitting a signal such as, for example, conductivewires, conductive traces, optical waveguides, or the like. Thecontroller 208 may also comprise one or more network interface modules,to connect the volatile extraction unit 104 to a remote computing deviceor a remote computer network. The network interface module may compriseany wired or wireless networking hardware, such as a modem, LAN port,wireless fidelity (Wi-Fi) card, WiMax card, mobile communicationshardware, and/or other hardware for communicating with other networksand/or devices, such as other components within the ceramic articleproduction line 100. Thus, in some embodiments, the communicationpathway may facilitate the transmission of wireless signals, such asWiFi, Bluetooth, and the like.

In some embodiments, the LFL detector 206 and the controller 208 operateto provide LFL controls for the volatile extraction unit 104. Forexample, a maximum LFL setpoint may be established and stored within thememory of the controller 208. The maximum LFL setpoint may be, in someembodiments, about 50% or between about 30% and about 40%, and may varyon the particular temperature within the volatile extraction unit 104 ata given time. When the LFL level measured by the LFL detector 206exceeds (i.e., is greater than) the maximum LFL setpoint, the controller208 may cause the O₂ concentration within the process atmosphere in thevolatile extraction unit 104 to be decreased, the heating rate to bedecreased, or both. The heating rate may be decreased, by way of exampleand not limitation, by slowing the heating rate, by reducing a hold timeor temperature, by holding the temperature for a particular period oftime, or even creating a cooling period (e.g., a negative heating rate).Accordingly, the controller 208 may be configured to adjust one or moreconditions within the volatile extraction unit 104 in response to thecomparison between the measured LFL level and the maximum LFL setpoint.

The heat source 210 may be configured to provide convective, conductive,or radiant heat, including but not limited to electric resistance,microwave, gas heating, or a combination thereof. The heat source 210provides combustion air to the volatile extraction unit 104 via a heatinlet 214. In some embodiments, a blower 216 is positioned near the heatinlet 214 to circulate the heat within the volatile extraction unit 104.Additionally, in various embodiments, a temperature sensor (not shown)may be integrated with the heat source 210, although it is contemplatedthat the temperature sensor may be a standalone sensor. In variousembodiments, the temperature sensor is configured to sense thetemperature within the volatile extraction unit 104 and provide feedbackto the controller 208.

The gas source 212 may comprise recirculated products of combustion(e.g., water vapor, nitrogen (N₂) gas and carbon dioxide (CO₂) gas),nitrogen (N₂) gas and air, any inert or noble gas such as helium, neon,and argon, or any gas containing a low level of oxygen (O₂) such as N₂gas or CO₂ gas. Although a single gas source 212 is depicted in FIG. 2 ,it is contemplated that multiple gas sources may be employed to providethe volatile extraction unit 104 with a low-oxygen process atmosphereand to enable the oxygen concentration within the process atmosphere tobe increased after the ceramic green body is cooled, as will bedescribed in greater detail below.

In some embodiments, the volatile extraction unit 104 may comprise ascale configured to measure the weight of the ceramic green body duringthe volatile extraction cycle. The scale may be communicatively coupledto the controller 208 such that the controller 208 may receive and storethe weight of the ceramic green body over time. In embodiments in whichthe volatile extraction unit 104 includes a scale, the time for thevolatile extraction cycle may be based at least in part on an amount ofweight loss of the ceramic green body or on a rate of weight loss of theceramic body, as will be described below.

In operation, one or more ceramic green bodies are positioned within thevolatile extraction unit 104. The controller 208 adjusts the processatmosphere by causing the gas source 212 to provide gas such that theprocess atmosphere is from about 2% to about 7% oxygen (O₂) by volume.In some embodiments, gas source 212 provides sufficient gas such thatthe process atmosphere is from about 2% to about 7% or from about 4% toabout 6% O₂ by volume of the process atmosphere. For example, the gassource 212 may inject a low oxygen gas, such as a nitrogen or CO₂enriched gas into the volatile extraction unit 104 through the gasinjection port 202.

In various embodiments, the controller 208 additionally causes the heatsource 210 to begin heating the process atmosphere. In variousembodiments, the controller 208 causes the heat source 210 to increasethe temperature of the process atmosphere within the volatile extractionunit 104 from room temperature to a temperature (e.g., a maximum debindtemperature) of from about 225° C. to about 400° C., from about 250° C.to about 350° C., or from about 225° C. to about 300° C. In embodiments,the temperature to which the process atmosphere is heated may bereferred to as a hold temperature, such as when the temperature withinthe volatile extraction unit will be held at the target temperature fora period of time.

As will be described in greater detail below, the controller 208 maycause the heat source 210 to hold the temperature within the volatileextraction unit 104 for a period of time sufficient to allow theconcentration of volatiles or the rate of weight loss to reach theirpeak and, in some embodiments, for a period of time sufficient for thepeak volatile concentration or rate of weight loss to have reduced by atleast about 10%, at least about 25%, at least about 30%, or even atleast about 50%. The hold time may be about 1 hour, about 2 hours, about3 hours, about 4 hours, or even about 5 hours. In embodiments in which ahold is utilized, the hold time may be from about 0 hours to about 4hours, from about 2 hours to about 3.5 hours, or the like. However, insome embodiments, the concentration of volatiles or the rate of weightloss may reach their peak or be reduced by at least about 10%, at leastabout 25%, at least about 30%, or even at least about 50% of the peakvalue during the ramp up to a predetermined temperature. In suchembodiments, a hold may not be utilized.

The heating rate may be greater than or equal to about 50° C. per hour(° C./hr.). For example, in some embodiments, the heating rate may befrom about 50° C./hr. to about 200° C./hr., from about 60° C./hr. toabout 130° C./hr., or from about 75° C./hr. to about 125° C./hr. Invarious embodiments, the heating rate may be less than or equal to about200° C./hr., less than or equal to about 130° C./hr., less than or equalto about 125° C./hr., or even less than or equal to about 80° C./hr. Insome embodiments, the heating rate may be about 75° C./hr., about 100°C./hr., or even about 125° C./hr. The heating rate may be limited to200° C./hr. or less in some embodiments. In embodiments, the particularheating rate employed may depend at least in part on the size of theceramic green body, the constituents within the ceramic batch mixtureused to form the ceramic green body, and the shape of the ceramic greenbody.

While the ceramic green body is heated in the volatile extraction unit104 through exposure to the process atmosphere within that unit, the LFLdetector 206 measures the LFL level, or combustible concentration, ofthe process atmosphere in the volatile extraction unit 104. Inembodiments, the LFL level is continuously measured. The LFL detector206 provides the measured LFL level to the controller 208, which storesthe LFL levels in a database. In various embodiments, the LFL levelsover time may be displayed on a display device (not shown) coupled tothe controller 208.

As provided hereinabove, the minimum hold time for a volatile extractioncycle may be determined by the LFL or by weight loss. As used herein,the “hold time” refers to the period of time during which thetemperature within the volatile extraction unit is maintained at atarget temperature. FIG. 3 depicts the temperature 302, the LFL curve304, the measured weight loss 306, the modeled weight loss 308, and theweight loss rate (dW/dt) 310 for an example volatile extraction cycleover time, as indicated in hours (hr) on the horizontal axis of thegraph. The left-hand vertical axis of FIG. 3 provides a temperature,indicated in ° C., and LFL scale, indicated in % times 10, for the LFLlevels within the process atmosphere. The right-hand vertical axis ofFIG. 3 provides a normalized weight loss scale, represented as a rate ofweight loss, dW/dt.

As shown in FIG. 3 , the temperature 302 of the process atmosphere isramped up from about room temperature to a hold temperature of about240° C. over a period of about two hours and held at about 240° C. forabout 8 hours. During that time, the LFL curve 304 (values shown in FIG.3 as percentages (%) scaled up by a factor of 10), begins at about 8%,then drops to about 5% before peaking at about 8% at an elapsed time of3 hours. The measured weight loss 306 exhibits a sharp drop between theelapsed time of 2 and 4 hours. A modeled weight loss 308 was fit to themeasured weight loss 306 and used to determine a weight loss rate 310.The peak in the weight loss rate 310 at the elapsed time of 3 hourscorresponds to the sharp drop in the measured weight loss 306 between 2and 4 hours. In various embodiments, the minimum hold time may beselected as the time at which the LFL curve 304 and/or the weight lossrate 310 peak. In other embodiments, the minimum hold time may beselected as the time at which the LFL curve 304 and/or the weight lossrate 310 reach an amount equal to 50% of the peak level.

Volatilized organic materials, sometimes referred to as volatile organiccomponents or simply “volatiles,” extracted from the ceramic green bodymay be exhausted through the exhaust port 204. In various embodiments,the volatilized organic materials may be processed before beingexhausted to the atmosphere. For example, the volatilized organicmaterials may be treated using thermal oxidizers, LFL controls, LOCcontrols, or the like to meet environmental regulations. In someembodiments, at least a portion of the volatilized organic materials maybe recycled or reclaimed. For example, extrusion oils that arevolatilized may be reclaimed.

After at least a portion of organic material has been extracted from theceramic green body, in various embodiments, the ceramic green body iscooled to a temperature below about 200° C. For example, the temperatureof the process atmosphere may be decreased from the hold temperatureafter the peak LFL has been reached or after the peak LFL has beenreached and the LFL has decreased to 50% or less of the peak LFL. Asanother example, the temperature of the process atmosphere may bedecreased from the hold temperature after a target weight loss has beenreached, after the peak weight loss rate has been reached, or after thepeak weight loss rate has been reached and the weight loss rate hasdecreased to 50% or less of the peak weight loss rate.

In some embodiments, the ceramic green body is cooled to a temperaturebelow about 190° C., below about 180° C., below about 170° C., belowabout 160° C., or even below about 150° C. For example, the ceramicgreen body may be cooled to a temperature between room temperature andabout 200° C., between room temperature and about 175° C., or betweenroom temperature and about 150° C. In various embodiments, the ceramicgreen body is cooled by cooling the process atmosphere to which theceramic green body is exposed.

Once the ceramic green body is cooled, oxygen may be reintroduced to theprocess atmosphere. For example, once the ceramic green body reaches atemperature below about 200° C., the amount of O₂ in the processatmosphere may be increased to a concentration substantially equivalentto ambient concentration. For example, the amount of O₂ may be increasedto a concentration of greater than 15% by volume or about 20.9% byvolume of the process atmosphere. Oxygen levels may be increased byadding oxygen to the process atmosphere using a gas source, or theprocess atmosphere may be slowly opened to the environmental atmosphere,such as through an inlet valve. Without being bound by theory, coolingthe ceramic green body to a temperature below about 200° C. beforeincreasing the concentration of O₂ in the process atmosphere may preventcombustion of the ceramic green body in the volatile extraction unit. Insome embodiments, the ceramic green body may be maintained in anatmosphere containing greater than 15% O₂ by volume for further cooling.

After the amount of O₂ in the process atmosphere is returned to a levelcomparable to atmospheric concentrations of O₂, in various embodiments,the ceramic green body may be transferred into the kiln 106 for firing.

As another example, the ceramic green body is positioned within thevolatile extraction unit 104. The controller 208 causes the gas source212 to provide gas sufficient to adjust the process atmosphere such thatthe process atmosphere is from about 2% to about 7% oxygen (O₂) byvolume. For example, the gas source 212 may inject a low oxygen gas,such as a nitrogen or CO₂ enriched gas into the volatile extraction unit104 through the gas injection port 202.

The controller 208 additionally causes the heat source 210 to beginheating the ceramic green body to increase the temperature within theprocess atmosphere from room temperature to a first hold temperature offrom about 140° C. to about 180° C., where the ceramic green body isheld for a first period of time, and then increase the temperature ofthe process atmosphere to a second hold temperature of from about 225°C. to about 400° C. In embodiments, the first hold temperature and thesecond hold temperature (e.g., the maximum debind temperature) canextend over a debind temperature range (e.g., from 100 C to 400 C) forthe process atmosphere. Without being bound by theory, it is believedthat exposing the ceramic green body to a process atmosphere heated tothe first temperature may be sufficient to volatilize extrusion oilssuch as mineral oil, and heating the process atmosphere to the secondtemperature may be sufficient to volatilize binders and starches. Aswill be described in greater detail herein, the controller 208 may causethe heat source 210 to hold the temperature within the volatileextraction unit 104 for a period of time sufficient to allow theconcentration of volatiles or the rate of weight loss to reach theirpeak and, in some embodiments, for a period of time sufficient for thepeak volatile concentration or rate of weight loss to have reduced by atleast about 10%, at least about 25%, at least about 30%, or even atleast about 50%.

The heating rate may be greater than or equal to about 50° C. per hour(° C./hr.). For example, the heating rate may be from about 50° C./hr.to about 200° C./hr., from about 60° C./hr. to about 130° C./hr., orfrom about 75° C./hr. to about 125° C./hr.

While the ceramic green body is heated in the volatile extraction unit104, the LFL detector 206 measures the LFL level, or combustibleconcentration, of the process atmosphere in the volatile extraction unit104. Volatilized organic materials are exhausted through the exhaustport 204. The volatilized organic materials may be treated using thermaloxidizers, LFL controls, LOC controls, or the like to meet environmentalregulations.

After a suitable portion of organic materials has been extracted fromthe ceramic green body, the ceramic green body is cooled to atemperature between room temperature and about 200° C., between roomtemperature and about 175° C., or between room temperature and about150° C.

Once the ceramic green body is cooled, oxygen is reintroduced to theprocess atmosphere such that the amount of O₂ in the process atmospherereaches a concentration of about 20.9% by volume of the processatmosphere. After the amount of O₂ in the process atmosphere is returnedto a level comparable to atmospheric concentrations of O₂, in variousembodiments, the ceramic green body may be transferred into the kiln 106for firing.

In embodiments in which at least a portion of the organic materials arevolatilized from the ceramic green body prior to firing, the firingcycles may be shortened compared to conventional firing cycles. Forexample, in some embodiments, the firing cycles may be reduced by anamount of time equal to a length of time of the volatile extractioncycle. Accordingly, although the total amount of time may be equivalent,embodiments in which the volatile extraction step is included may resultin less time in the kiln, which in turn may increase the availability ofthe kiln. Moreover, in some embodiments, one volatile extraction unit104 may feed multiple kilns in a ceramic article production line.

EXAMPLE

The various embodiments described hereinabove will be further clarifiedby the following example.

Ten ceramic green bodies for forming light duty ceramic cordieritefilters were subjected to a volatile extraction cycle. The processconditions for the volatile extraction cycle are presented in Table 1.The temperature (in ° C.), LFL level (in %), and oxygen concentration(in %) are shown as a function oftime (in hours) for the volatileextraction cycle are depicted in FIG. 4 . Specifically, the left-handvertical axis provides a temperature, in ° C., while the right-handvertical axis provides a LFL and oxygen (O₂) concentration by volume,both in percentages (%). Elapsed time, in hours (hr.) is provided alongthe horizontal axis. As shown by plot 402, the average temperature inthe volatile extraction unit was increased from about room temperature(i.e., about 23° C.) to a temperature of 250° C. The temperature washeld at 250° C. for two (2) hours before it is decreased. As shown byplot 404, the process atmosphere had an oxygen concentration of about 4%during the volatile extraction cycle. Plot 406 represents the LFL levelmeasured within the volatile extraction unit. As shown in FIG. 4 , theLFL curve peaked at about 14% just before an elapsed time of four (4)hours, and then decreased. Notably, the LFL curve represented by plot406 came down to a baseline level of about 12% near the end of thetemperature hold, indicating that the volatile release was nearcompletion.

Following the volatile extraction cycle, the ten ceramic green bodieswere transferred to a kiln and subjected to a firing cycle. Tenadditional ceramic green bodies which were not subjected to a volatileextraction cycle were subjected to a separate firing cycle as a control.The process conditions and results for the volatile extraction andfiring cycles are provided in Table 1 below.

TABLE 1 Process Conditions and Results Volatile Extraction and FiringFiring only (Control) Part size 4.66 × 6″ 4.66 × 6″ Sample size 10 10Volatile Extraction Cycle Conditions Hold Temperature 250° C. n/a HoldOxygen Level   4% n/a Hold Time 2 hr. n/a Firing Cycle Conditions FiringHeating Rate 125° C./hr. 125° C./hr. (room temperature to 900° C.)Firing O₂ set point   18%   18% Crack Rate 0/10 0/10 LFL (%) 3.80% 9.60%

During the firing cycle, the LFL levels were measured. The results areshown in FIG. 5 . The left-hand vertical axis of FIG. 5 provides atemperature, in ° C., while the right-hand vertical axis provides a LFLlevel, in percentages (%). Elapsed time, in hours (hr.) is providedalong the horizontal axis. In FIG. 5 , the LFL curve 502 for the ceramicgreen bodies that were not subjected to the volatile extraction cycle(i.e., the control wares) shows a sharp LFL peak at about 3 hours whilethe temperature (represented by plot 506) is being ramped up. Asreported in Table 1, this peak corresponds to a LFL of 9.60%. However,the LFL curve 504 for the ceramic green bodies that were subjected tothe volatile extraction cycle (i.e., the exemplary wares) does not showa LFL peak. FIG. 5 demonstrates that the use of the volatile extractioncycle prior to firing is effective to reduce the LFL levels releasedduring firing. In particular, FIG. 5 suggests that because the LFL levelremains below about 4.5% and has an average level of about 3.8%, the LFLcontrols, LOC controls, and other controls conventionally necessitatedby environmental regulations related to volatilization of organicmaterials may be removed from the kiln when the ceramic green bodies arefirst subjected to a volatile extraction cycle.

Thus, the firing of ceramic green bodies to convert them to ceramicarticles can include the debinding or removal from the bodies of variousorganic binding or pore-forming constituents. Those constituents areemployed in the forming stage of manufacture to facilitate shaping ofplastic mixtures of ceramic precursor powders and binding constituentsinto self-supporting ceramic green bodies. The embodiments of thepresent disclosure can address significant manufacturing difficultiesthat can arise with known processes and equipment, such as where theceramic green bodies include more than about 5% by weight of organicconstituents such as cellulosic binders and/or pore forming additives,such as starch, that, are combustible. High rates of cracking couldresult in fired ware if the removal of organic binding and/orpore-forming constituents is not carefully managed. The debinding oflarge ceramic green bodies, such as those used for the production ofcordierite particulate filters for treating heavy duty diesel engineexhaust streams, can be particularly problematic, and can be addressedby one or more embodiments of the present invention. In addition, theorganic binding and/or pore-forming constituents may produce volatilesas they are released from the ceramic green body. In contrast, variousembodiments described herein may be employed to extract or debindvolatiles or organic material from ceramic green bodies prior to firingthe ceramic green bodies to produce ceramic articles. Removal of atleast some of the organic material from the ceramic green bodies in avolatile extraction unit prior to firing at higher oxygen levels and atfaster firing rates may reduce average and peak LFL levels, therebypreferably eliminating the need for kilns to be provided with expensiveequipment such as atmospheric controls, thermal oxidizers, LFL controlsand/or LOC controls which are conventionally employed to meetenvironmental regulations. This can, in turn, reduce capital costsassociated with kilns. Moreover, because a single volatile extractionunit, which may have a shorter processing cycle as compared to aconventional kiln, may feed multiple kilns in a ceramic articleproduction line, manufacturing throughput of ceramic articles may beincreased.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the embodiments describedherein without departing from the spirit and scope of the claimedsubject matter. Thus it is intended that the specification cover themodifications and variations of the various embodiments described hereinprovided such modification and variations come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of producing a ceramic article, themethod comprising: extracting organic material from a ceramic green bodyby heating the ceramic green body, the extracting comprising heating thegreen body in a low oxygen debind atmosphere having a debind temperaturerange of from 100° C. to 400° C., wherein the low oxygen debindatmosphere is 2% to 7% O₂ by volume, and wherein the debind temperaturerange comprises a maximum debind temperature in a range of from 225° C.to 400° C.; then cooling the ceramic green body from the maximum debindtemperature to a temperature below 200° C.; after the ceramic green bodyis cooled to a temperature below 200° C., firing the ceramic green bodyinto the ceramic article by exposing the ceramic green body to a firingatmosphere which has a higher concentration of O₂ than the low oxygendebind atmosphere.
 2. The method of claim 1 wherein the ceramic greenbody is cooled in an atmosphere which is 2% to 7% O₂ by volume.
 3. Themethod of claim 1 wherein a first portion of the organic material isremoved from the ceramic green body during the extracting, and a secondportion of the organic material is removed during the firing.
 4. Themethod of claim 1 wherein the firing comprises increasing a temperatureof the firing atmosphere at a rate greater than 50° C./hr.
 5. The methodof claim 1 wherein the firing comprises increasing a temperature of thefiring atmosphere at a rate greater than 50° C./hr and less than 200°C./hr.
 6. The method of claim 1 wherein the temperature of the debindatmosphere is reduced to below the maximum debind temperature after apeak lower flammability limit (LFL) has been reached during theextracting.
 7. The method of claim 1 wherein the temperature of thedebind atmosphere is reduced to below the maximum debind temperatureafter a peak lower flammability limit (LFL) has been reached during theextracting and after the LFL in the low oxygen debind atmosphere hasdecreased to 50% or less of the peak LFL.
 8. The method of claim 1further comprising measuring a lower flammability limit (LFL) in the lowoxygen debind atmosphere and controlling a duration of exposure of theceramic green body to the maximum debind temperature based on LFLmeasurement.
 9. The method of claim 1 wherein the temperature of thedebind atmosphere is reduced to below the maximum debind temperatureafter a target weight loss of the ceramic green body is reached.
 10. Themethod of claim 1 wherein at least 30% of an original organic materialcontent in the ceramic green body is removed during the extracting step.11. The method of claim 1 wherein the ceramic green body is exposed tothe maximum debind temperature for 0.01 to 4 hours.
 12. The method ofclaim 1 wherein the debind atmosphere is held to within 25° C. of themaximum debind temperature for 0.01 to 4 hours.
 13. The method of claim1 wherein the ceramic green body is exposed to the low oxygen debindatmosphere for 1 to 10 hours.
 14. The method of claim 1 furthercomprising measuring a lower flammability limit in the debindatmosphere, wherein the ceramic green body is heated in the debindatmosphere for a time sufficient for the lower flammability limit in thedebind atmosphere to reach a peak level.
 15. The method of claim 14wherein the ceramic green body is heated for a time sufficient for thelower flammability limit to decrease to an amount of at least 50% of thepeak level.
 16. The method of claim 1 wherein the debind maximumtemperature is from 250° C. to 350° C.
 17. The method of claim 1 whereinthe debind atmosphere is 4% to 6% O₂ by volume.
 18. The method of claim1 wherein the extracting step is performed in a first kiln, and thefiring step is performed in a second kiln which is different from thefirst kiln.
 19. The method of claim 1, wherein the ceramic green bodycomprises a plurality of green ceramic bodies each comprising organicmaterial, and wherein the organic material is extracted from theplurality of green ceramic bodies in a first kiln, and a first subset ofthe plurality of green ceramic bodies is fired in a second kiln,different from the first kiln, and a second subset of the plurality ofgreen ceramic bodies is fired in a third kiln, different from the firstand second kilns.
 20. The method of claim 1 wherein the organic materialcomprises a plurality of organic materials.